We would like to inform you about a vulnerability in personal firewalls and HIPS software.

Description:

Windows operating systems with NT kernel version 5.0 and higher (i.e. Windows 2000, XP, 2003) use integer numbers
divisible by four to identify processes. Internal implementation of system API functions also allows programmers to use
integers that are not divisible by four. This means that for every process running in the system there are four valid
identifiers.

The control of API functions, which work with process identifiers, like OpenProcess (usually implemented by SSDT hook of
NtOpenProcess), that assumes using identifiers divisible by four is insufficient. An implementation by a simple test on
equivalence between the internal personal firewall/HIPS database and the given identifier can be dangerous. In such
case, it is possible that a firewall misinterprets a call and allows an action that should be forbidden. If the security
software implements a process protection for critical processes in this manner, it is a critical bug, which can be
exploited to gain control over the whole system. Vulnerable products implements process protection, which can be
bypassed if identifiers not divisible by four are used.